LPTHW 练习 48 帮助 - 列表中的元组操作

Question

我现在正在学习《通过艰难的方式学Python》，已经到了第48个练习，这是我第一次遇到瓶颈。

这是我收到的测试案例的第一部分：

from nose.tools import *
from ex48 import lexicon

def test_direction():
    assert_equal(lexicon.scan("north"), [('direction', 'north')])
    result = lexicon.scan("north south east")
    assert_equal(result, [('direction', 'north'),
                          ('direction', 'south'),
                          ('direction', 'east')])

这个问题之前有人问过，我发现我现在的解决方案和robbyt提供的答案几乎一模一样。但它还是不管用。

def scan(thewords):

    directions = [('direction', 'north'), ('direction', 'south'), ('direction', 'east')]

    thewords = thewords.split()
    sentence = []

    for i in thewords:
        if i in directions:
            sentence.append(('direction', i))

        else:
            sentence.append(('error', i))


    return sentence

所以问题是：在获取输入（thewords）后，我该如何正确地在元组列表中搜索，然后返回它所属于的特定元组呢？

非常感谢任何形式的回答和建议，我真的被这个问题困住了。

Answer 1

使用字典会让事情变得简单又快速。看看这段代码吧。

directions = ['north', 'south', 'east', 'west', 'down', 'up', 'left', 'right', 'back']
verbs = ['go','stop','kill','eat']
stop_words = ['the', 'in', 'of', 'from', 'it']
nouns = ['door','bear','princess','cabinet']

lexicons = {}
for key in directions:
    lexicons[key] = 'direction'
for key in verbs:
    lexicons[key] = 'verb'
for key in stop_words:
    lexicons[key] = 'stop'
for key in nouns:
    lexicons[key] = 'noun'

def scan(sentence):
    tuples = []
    words = sentence.split()
    for word in words:
        try:
            tuples.append((lexicons[word],word))
        except KeyError:
            if word.isdigit():
                tuples.append(('number',int(word)))
            else:
                tuples.append(('error',word))
    return tuples

Answer 2

受到@Evee第一个解决方案的启发（谢谢你），这是我的解决方案，它通过了所有的测试。也许它的代码比第二个解决方案多一些，但它省去了在唯一定义的方法外面使用循环。

class Lexicon(object):
    def __init__(self):
        self.mapping = {
              'direction':  ['north', 'south', 'east', 'west'],
              'verb':       ['go', 'kill', 'eat'],
              'stop':       ['the', 'in', 'of'],
              'noun':       ['door', 'bear', 'princess', 'cabinet']
              }
        self.mapping_categories = self.mapping.keys()

    def scan(self, input):
        self.result = []

        for word in input.split():
            try:
                self.result.append(('number', int(word)))
            except ValueError:
                for category, item in self.mapping.items():
                    if word.lower() in item:
                        found_category = category
                        break
                    else:
                        found_category = 'error'
                self.result.append((found_category, word))

        return self.result

lexicon = Lexicon()

Answer 3

所以多亏了Thomas K和ed的提示，我终于完成了这个练习。现在回头看，我有点懊恼自己，因为其实这件事看起来是如此简单……

directions = ['north', 'south', 'east', 'west', 'down', 'up', 'down', 'right']
verbs = ['go', 'stop', 'kill', 'eat']
stops = ['the', 'in', 'at', 'of', 'from', 'at', 'it']
nouns = ['door', 'bear', 'princess', 'cabinet']


def scan(thewords):

    thewords = thewords.split()
    sentence = []

    for i in thewords:
        if i in directions:
            sentence.append(('direction', i))

        elif i in verbs:
            sentence.append(('verb', i))

        elif i in stops:
            sentence.append(('stop', i))

        elif i in nouns:
            sentence.append(('noun', i))

        elif i.isdigit():
            sentence.append(('number', convert_number(i)))

        else:            
            sentence.append(('error', i))

    return sentence

def convert_number(s):
    try:
        return int(s)

    except ValueError:
        return None